Semiconductor device and method for fabricating the same

ABSTRACT

A method for fabricating semiconductor device includes the steps of: providing a substrate having a memory region and a logic region; forming a stack structure on the memory region and a gate structure on the logic region; forming a first cap layer on the stack structure and the gate structure; performing an oxidation process to form an oxide layer on the first cap layer; forming a second cap layer on the oxide layer; and removing part of the second cap layer, part of the oxide layer, and part of the first cap layer on the logic region to form a spacer adjacent to the gate structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 15/952,182filed Apr. 12, 2018, and incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method for fabricating semiconductor device,and more particularly, to a method of using oxidation process to formoxide layer on a cap layer on memory region.

2. Description of the Prior Art

As electronic products develop toward the direction of miniaturization,the design of dynamic random access memory (DRAM) units also movestoward the direction of higher integration and higher density. Since thenature of a DRAM unit with buried gate structures has the advantage ofpossessing longer carrier channel length within a semiconductorsubstrate thereby reducing capacitor leakage, it has been gradually usedto replace conventional DRAM unit with planar gate structures.

Typically, a DRAM unit with buried gate structure includes a transistordevice and a charge storage element to receive electrical signals frombit lines and word lines. Nevertheless, current DRAM units with buriedgate structures still pose numerous problems due to limited fabricationcapability. Hence, how to effectively improve the performance andreliability of current DRAM device has become an important task in thisfield.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a method forfabricating semiconductor device includes the steps of: providing asubstrate having a memory region and a logic region; forming a stackstructure on the memory region and a gate structure on the logic region;forming a first cap layer on the stack structure and the gate structure;performing an oxidation process to form an oxide layer on the first caplayer; forming a second cap layer on the oxide layer; and removing partof the second cap layer, part of the oxide layer, and part of the firstcap layer on the logic region to form a spacer adjacent to the gatestructure.

According to another aspect of the present invention, a semiconductordevice includes: a substrate having a memory region and a logic region,a gate structure on the logic region, and a first spacer around the gatestructure. Preferably, the first spacer further includes a first caplayer, an oxide layer on the first cap layer, and a second cap layer onthe oxide layer.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 illustrate a method for fabricating a semiconductor deviceaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1-5, FIGS. 1-5 illustrate a method for fabricating asemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 1, a substrate 12 such as a siliconsubstrate or silicon-on-insulator (SOI) substrate is provided. At leasta memory region 14 (or cell region) and a logic region 16 (or peripheryregion) are defined on the substrate 12, in which the memory region 14is defined to fabricate DRAM device having buried gates and the logicregion 16 is defined to fabricate active devices such as metal-oxidesemiconductor (MOS) transistors.

In this embodiment, a plurality of buried gate structures 18 could beformed in the substrate 12 on the memory region 14, at least a shallowtrench isolation (STI) 20 could be formed in the substrate 12 to divideelements between the memory region 14 and the logic region 16, and eachof the STI 20 and an insulating material formed on the substrate 12 onthe memory region 14 could include a silicon oxide layer 22, a siliconnitride layer 24, and another silicon oxide layer 26.

Next, a stack structure 28 is formed on the memory region 14 and atleast a gate structure 30 is formed on the logic region 16, in which thestack structure 28 is disposed on the substrate 12 on memory region 14and covering a plurality of buried gate structures 18 within thesubstrate 12 while the gate structures 30 on the logic region 16 isdisposed on the surface of the substrate 12. In this embodiment, theformation of the stack structure 28 and the gate structures 30 could beaccomplished by sequentially forming a plurality of material layers (notshown) on the substrate 12 on both the memory region 14 and logic region16, in which the material layers could include an amorphous siliconlayer 32, a titanium (Ti) layer 34, a titanium nitride (TiN) layer 36, atungsten silicide (WS) layer 38, a tungsten (W) layer 40, a siliconnitride layer 42, and a silicon oxide layer 44. Next, a pattern transferor photo-etching process is conducted by using a patterned resist (notshown) as mask to remove part of the above material layers to form astack structure 28 and gate structures 30 on the memory region 14 andlogic region 16 respectively.

Next, a first cap layer 46 is formed on the stack structure 28, the gatestructures 30, and the STI 20 and an oxidation process is conducted tooxidize part of the first cap layer 46 for forming an oxide layer 48 onthe first cap layer 46. In this embodiment, the first cap layer 46preferably includes silicon carbon nitride (SiCN) and the oxide layer 48fabricated through the aforementioned oxidation process preferablyincludes silicon carbon oxynitride (SiCON).

Next, as shown in FIG. 2, a second cap layer 50 is formed on the oxidelayer 48, a patterned mask such as patterned resist 52 is formed on thememory region 14, and an etching process is conducted by using thepatterned resist 52 as mask to remove part of the second cap layer 50,part of the oxide layer 48, and part of the first cap layer 46 on thelogic region 16 to form a first spacers 54 on sidewalls of the gatestructures 30. In this embodiment, each of the first spacers 54preferably includes a first cap layer 46 having L-shaped cross-section,an oxide layer 48 having L-shaped cross-section, and a second cap layer50 having I-shaped cross-section, in which the second cap layer 50preferably includes silicon nitride, but not limited thereto.

Next, at least an ion implantation process is conducted by using thepatterned resist 52 on the memory region 14 and the gate structures 30and first spacer 54 on the logic region 16 as mask to implant ions intothe substrate 12 adjacent to two sides of the first spacer 54 forforming a doped region (not shown) serving as lightly doped drain (LDD)or source/drain region, in which the lightly doped drain could includen-type or p-type dopants depending on the type of transistor beingfabricated.

Next, as shown in FIG. 3, after stripping the patterned resist 52 on thememory region 14, a third cap layer 56 is formed on the stack structure28 and the gate structures 30, in which the third cap layer 56preferably includes silicon oxide, but not limited thereto.Specifically, the third cap layer 56 preferably covers the exposedsurface of the second cap layer 50 on the memory region 14 and thesurface of the gate structures 30 and first spacer 54 on the logicregion 16. Next, another patterned mask such as patterned resist 58 isformed on the third cap layer 56 the logic region 16 to expose the thirdcap layer 56 on the memory region 14.

Next, as shown in FIG. 4, an etching process is conducted by using thepatterned resist 58 as mask and using a first etchant comprising dilutedhydrofluoric acid (dHF) to remove the third cap layer 56 on the memoryregion 14 and expose the surface of the second cap layer 50 underneath.The remaining third cap layer 56 on the logic region 16 then becomes asecond spacer 60 and the second spacer 60 covers the top surface of thegate structures 30 and sidewalls of the first spacer 54.

Next, as shown in FIG. 5, another etching process is conducted by usingthe patterned resist 58 as mask and using a second etchant comprisingphosphoric acid to remove the second cap layer 50 on the memory region14, and the patterned resist 58 is stripped thereafter. It should benoted that since the second cap layer 50 made of silicon nitride isdisposed directly on top of the first cap layer 46 made of SiCN inconventional approach with no oxide layer 48 formed between the two caplayer 46 and 50, the surface of the first cap layer 46 made of SiCNunderneath is easily damaged by the etchant primarily consisting ofphosphoric acid during the removal of the second cap layer 50 made ofsilicon nitride on the memory region 14. By conducting theaforementioned oxidation process to first form an oxide layer 48 made ofSiCON serving as a stop layer on the surface of the first cap layer 46,the present invention is able to stop the etching process usingphosphoric acid as etchant right on the oxide layer 48 as soon as thesecond cap layer 50 on the memory region 14 is removed so that none ofthe first cap layer 46 underneath would be damaged.

Next, a photo-etching process could be conducted to pattern the stackstructure 28 on the memory region 14 to form one or more bit linestructures and contact structures such as storage node contacts could beformed adjacent to two sides of the bit line structures on the memoryregion 14 to electrically connect source/drain region and capacitorsformed in the later process and contact plugs could be formed adjacentto two sides of the gate structures 30 on the logic region 16. Thiscompletes the fabrication of a semiconductor device according to anembodiment of the present invention.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method for fabricating semiconductor device,comprising: providing a substrate having a memory region and a logicregion; forming a shallow trench isolation (STI) between the memoryregion and the logic region; forming buried gate structures in thesubstrate on the memory region; forming a stack structure on the buriedgate structures on the memory region and a gate structure on the logicregion, wherein the STI is between the stack structure and the gatestructure and the gate structure comprises: a semiconductor layer; ametal layer on the semiconductor layer; and a dielectric layer on themetal layer; forming a first cap layer on the stack structure and thegate structure; performing an oxidation process to form an oxide layeron the first cap layer; forming a second cap layer on the oxide layer;and removing part of the second cap layer, part of the oxide layer, andpart of the first cap layer on the logic region to form a spaceradjacent to the gate structure.
 2. The method of claim 1, furthercomprising: forming a third cap layer on the stack structure and thegate structure; forming a patterned mask on the logic region; andremoving the third cap layer and the second cap layer on the memoryregion.
 3. The method of claim 2, further comprising using a firstetchant to remove the third cap layer on the memory region.
 4. Themethod of claim 3, wherein the first etchant comprises dilutedhydrofluoric acid (dHF).
 5. The method of claim 2, further comprisingusing a second etchant to remove the second cap layer on the memoryregion.
 6. The method of claim 5, wherein the second etchant comprisesphosphoric acid.
 7. The method of claim 2, wherein the third cap layercomprises silicon oxide.
 8. The method of claim 1, wherein the first caplayer comprises silicon carbon nitride (SiCN).
 9. The method of claim 1,wherein the oxide layer comprises silicon carbon oxynitride (SiCON). 10.The method of claim 1, wherein the second cap layer comprises siliconnitride.